I don't think it is trivial functions...
Without checking release functions, I should write like this:

var key_w_release=off;
action PlayerAction()
{
while(1)
{
if(key_w && key_w_release==off)
{key_w_release=on;}
if(!key_w && key_w_release)
{
//other code
key_w_release=off;
}
wait(1);
}
}

I think this way is inconvenient.
with the release functions, I should only do this:
action PlayerAction()
{
while(1)
{
if(key_w_release)
{
//other code
}
wait(1);
}
}
Isn't this more concise?
Or just invent a general function to check if a key is released.
Such as check_key_release(key_w), return true or false.
Same as the mouse, check_mouse_release(mouse_left).